The surfaces of the keys of most keyboards, such as computer keyboards, bear identifying indicia--letters, numbers, symbols, or a combination thereof. Some keys include several indicia, each representing a different function. The state of a function control key, such as the shift key determines which of the functions a multifunction key is to perform and, thus, which indicia denotes the operative key function. As more functions are assigned to particular keys, more and more indicia are added. In order to separate indicia, some keyboards include function identifying indicia on the front as well as the top surface of the keys of the keyboard. This invention is directed to the creation of the function identifying indicia located on the top and front surfaces of the keys of a keyboard.
In the past, keyboard indicia have been created by various techniques. At one end of the spectrum of techniques lie expensive two-shot molding techniques (which create deeply imbedded, long wearing indicia). At the other end lie relatively inexpensive surface printing techniques (which create a surface image that wears away with time and use). Recently, keyboard manufacturers have begun to use dry diffusion printing techniques to create indicia in the tops of the keys. This technique has the advantages of creating diffused indicia images whose wear life is considerably greater than surface printed images at a cost substantially less than the cost of two-shot molding. In dry diffusion printing, a transfer paper onto which the image has been preset is pressed against the top of the key that is to receive the indicia. The pressure plus heat results in the dye that forms the indicia image being transferred from the transfer sheet to the key. A recently developed diffusion printer, described in U.S. patent application Ser. No. 725,924, filed Apr. 22, 1985, now abandoned and refiled as Ser. No. 888,646 on July 24, 1986 and entitled "Double Shuttle Diffusion Printer" by Brian K. Neil, assigned to the assignee of the present application, transfers images to several keys (including an entire keyboard) simultaneously. During transfer, the dry dye crystals that form the image sublimate upon heated contact with the resin that forms the key. That is, the dry dye crystals change directly from a solid form into a gas and back into a solid without going through a liquid phase. The attraction force between the dry dye crystals and the resin molecules "pull" the image onto the top surface of the keys. The end result of this migration is a sharp, abrasion-proof image infused to a depth of 4-6 mils. Since dry dye crystals are transferred directly from a pattern preset on the transfer paper, multicolored images can be transferred in a single step.
In the past, dry diffusion printing machines of the type described in the patent application referenced above, have been only able to apply images to the top surface of the keys. Other techniques have been required to apply images to the front surface of the keys of a keyboard. One method involves a wet printing process that uses epoxy or solvent based inks. The front surface of multifunction keys are individually printed in fixtures and, then, assembled into the keyboard. The entire keyboard is then top surface printed in a printer of the type described in the patent application referenced above. Because this procedure is labor intensive, it is expensive. Further, the repetitive nature resulting from printing individual keys and then assembling them in a keyboard in a particular location makes the probability of error high. The present invention is directed to avoiding these and other problems by providing an improved dry diffusion printing machine that simultaneously prints indicia into the top and one of the side (e.g., the front) surfaces of the assembled keys of a keyboard.